In geared elevator systems, the motor is coupled to the drive sheave through a worm reduction gear system. In a typical worm gear drive, the worm gear shaft is supported in the gear box housing by a pair of tapered roller bearings located at either end of the gear box housing. A cap bears against the outer race of each of the roller bearings, so as to pre-load the bearings in the axial direction, toward one another, by a specified amount. The caps also contain a seal.
More particularly, the front cap, which supports the outer race of the front tapered roller bearing, covers an opening in the gear box housing and seals the front end of the gear box housing with an "O" ring seal, which is disposed in an "O" ring groove formed in the cap. The rear cap, which is located on the motor side of the gear box housing, has a hole to allow the worm shaft to pass through. The rear cap seals the gear box housing and shaft with a smooth lip, bi-rotational, hydrodynamic shaft seal.
The front and rear caps are secured to the gear box housing by a plurality of mounting bolts. The distance between the front and rear caps (which controls the amount of pre-load on the bearings) is adjusted by using shims under the front cap.
Whenever the rear seal needs to be replaced, the rear cap needs to be removed, which changes the factory pre-load setting. As a result, it is necessary to reset the pre-load on the tapered roller bearings. Typically, the replacement rear seal is shipped from the factory pre-installed in a new rear cap accompanied by a new shim package for the front cap.
In order to reset the proper load, the front seal is removed and the old shims are removed and discarded. After the new rear cap and replacement seal assembly have been mounted onto the gear box housing, and the mounting bolts have been torqued to the specified setting, the front cap is first installed without any shims, and is torqued to a factory predetermined value. The gap between the front cap flange and the gear box housing is measured with feeler gauges at each mounting bolt location. The measured gaps are used to determine the quantity of shims required for proper worm shaft pre-load. The front cap is again removed and the required shims installed between the front cap flange and the gear box housing. The mounting bolts are torqued to specification, and the elevator can be returned to service.
As is evident from the foregoing description, replacing the rear dynamic seal of the worm gear box is a relatively lengthy procedure. While it is also necessary to reset the pre-load on the tapered roller bearings when the front seal is replaced, because the front seal is a static "O" ring replacement is required much less often.